90

CHAPTER 4

GROWTH AND CHARACTERIZATION OF DYES AND

AMINO ACID DOPED GLYCINE PHOSPHITE SINGLE

CRYSTALS

4.1 INTRODUCTION

Different combination of amino acids and inorganic acids lead to

invention of new crystal family with excellent ferroelectric properties.

Examples of such combinations are triglycine sulphate, triglycine selenate,

triglycine fluoberyllate, betaine phosphite and Glycine Phosphite (Alemany

et al 1973, Song et al 2000, Lines and Glass 1977, Albers et al 1988). Growth

and characterization of pure and thiourea doped GPI crystals were

investigated by several researchers (Deepthy and Bhat 2001, Kalainathan et al

2005, 2006). Doping of dyes in organic crystals such as KDP, KAP, bis

glycine cadmium chloride and L-arginine phosphate were reported to

understand the optical, thermal, NLO, laser applications and mechanical

properties of the materials (Monica Enculescu 2009, Pritula et al 2009,

Velikhov et al 2007, Kumaresan et al 2008, Raju et al 2011, Shivani Singh

and Bansi Lal 2008). Numerous efforts were made on the growth,

pyroelectric and ferroelectric properties of amino acid doped TGS crystals

(Lock 1971, Bye et al 1973, Alexandru et al 2004, Raghavan et al 2008,

Nakatani et al 2008, Meera et al 2000, 2001, 2004). Efforts were also made on

combinations of doping such as urea, yttrium sulfate, L-serine + cobalt

sulfate, and L-alanine + urea with TGS crystals. These combinations

91

effectively increase dielectric, pyroelectric, ferroelectric and mechanical

properties of the material (Jiann-Min Chang et al 2002, Jan Novotny et al

2003). Influence of L-Alanine and D-Alanine dopants on TGS improves the

ferroelectric and pyroelectric stabilities (Berbecaru et al 2005). Hence dyes

doped KDP and amino acid doped TGS crystals play a major role in

improving physical properties of the materials. Since GPI is the hydrogen

bonded ferroelectric material like TGS and soft ferroelectric material as that

of KDP crystals, in the present investigation, organic dyes such as rhodamine-

B, malachite green and fluroscein and amino acid (L-Proline) were doped

with pure GPI crystals to analyze the growth and physical properties of the

materials.

4.2 BULK CRYSTAL GROWTH

The impurity content of synthesized GPI was minimized by

purifying the solution by repeated recrystallization. In this study, 0.5 mol %

of organic dyes such as rhodamine-B, malachite green and fluroscein and 3

mol % amino acid (L-Proline) were doped with pure GPI crystals. Growth

runs were carried out from solution saturated at 45o C according to the

nucleation kinetic data, it is feasible to grow bulk crystals in 45o C to 40o C

range. The saturated solution was further purified by Wattman filter paper (42

grades). Before starting the growth, to ensure the homogenization of the

solution, it was heated to a few degrees above the saturation temperature. The

temperature was reduced at the rate of 0.2o C / day as the growth progressed.

The seeds obtained from slow evaporation were employed for the growth. The

test seed was used and seasoned at the growth temperature before initiating

the growth. Once the growth was initiated, the good quality (100) oriented

seeds were used for the growth. The period of growth ranges from 30 to 35

days. After the completion of growth, crystals were harvested. The grown

92

crystals were found to be non-hygroscopic. The crystal dimensions of RB-

GPI, M.grn-GPI, Flrn-GPI and L.Prol-GPI are 18 mm × 16 mm × 10 mm, 13

mm × 10 mm × 8 mm, 20 mm × 12 mm × 10 mm and 30 mm × 24 mm × 14

mm respectively and are shown in Figure 4.1.

(a) (b)

(c) (d)

Figure 4.1 As grown crystals of (a) Rhodamine-B and (b) Malachite

green doped GPI by solvent evaporation method and

(c) Fluorescein and (d) L-Proline doped GPI grown by slow

cooling method

93

4.3 RESULTS AND DISCUSSION

4.3.1 Single Crystal X-Ray Diffraction Analysis

Unit cell parmeters of dyes and amino acid doped GPI crystals were

determined by single crystal X-ray diffraction studies using ENRAF NONIUS

CAD 4 single crystal X-ray diffractometer with MoK ( =0.717 ) radiation

at room temperature. The crystal specimens of dimension 4×3×3 mm3 were

used for the analysis. Least-square refinement of 135, 163, 225 and 130

reflections were made for rhodamine-B, malachite green, fluorescein and L-

Proline doped GPI crystals respectively and the structure was solved by direct

method and refined by the full matrix least-square technique using the

SHELXL program. Dyes and amino acid doped GPI belong to monoclinic

structure with the space group P21/a at room temperature i.e in paraelectric

phase. The lattice parameters of pure and rare earth metals doped GPI crystals

were presented in Table 4.1. It was observed that volume of the doped

crystals decreased which attributes to the lattice strain by means of dyes and

amino acid as dopants.

Table 4.1 Lattice parameters of pure, dyes and amino acid doped GPI

crystals

CellParameters /

CrystalName

a (Å) b (Å) c (Å) V (Å3)

Pure GPI 7.391(2) 8.477(3) 9.774(4) 90o 100.48 o 90o 616

R.B-GPI 7.381(7) 8.441(8) 9.751(9) 90o 100.55 o 90o 597.3

M.grn-GPI 7.395(6) 8.474(7) 9.763(8) 90o 100.45 o 90o 601.7

Flrn-GPI 7.375(8) 8.446(11) 9.743(11) 90o 100.45 o 90o 596.8

L.Prol-GPI 7.378(8) 8.462(9) 9.753(10) 90o 100.35 o 90o 599

94

4.3.2 Powder X-Ray Diffraction Analysis

The powder X-ray diffraction pattern for dyes and amino acid

doped GPI crystals was recorded using SEIFERT JSO DEBYE FLEX 2002

diffractometer. The powdered samples of grown crystals were subjected to

intense X-rays of wavelength 1.5405 Å (CuK ) at scan speed of 1o/ min. The

powder diffraction pattern of pure, dyes doped GPI crystals are shown in

Figure 4.2. The changes in the relative intensity and peak position of the

pattern confirm the incorporation of dyes in pure GPI crystal. The intensity of

rhodamine-B doped GPI was predominantly suppressed as shown in Figure

4.2 and most of the planes after 30o were diminished in the case of malachite

green and fluorescein doped GPI samples.

20 30 40 50 600

200

400

600

0

10

20

30

400

200

400

600

8000

100

200

300

400

500

(402

)

(33-3

)

(30

3)

(14

1)

(302)

(320)

(13

2)

(11-4

)

(023)

(103

)

(013

)

(21

-1)

(11

2)

(20-1

)(1

20)

(11

-2)

(10

-2)

Degree (2 )

GPI

(12

-1)

(143)

(410

)

(32

1)

(30

-3)

(13

-2)

(211

)(2

01)

(21

-1)

(112)

(120

)

(11-2

)(0

20)In

ten

sit

y (

arb

.un

its

)

R.B-GPI

(112

)

(21

1)

(12

0)(1

1-2

)

M.grn-GPI

(13

3)

(21

1)

(112)

(120

)(1

1-2

)

Flrn-GPI

Figure 4.2 Powder XRD pattern of Pure, Rhodamine-B, Malachite

green, and Fluorescein doped GPI crystals

95

4.3.3 Crystalline Perfection Analysis

Crystalline Perfection of dyes and amino acid doped GPI crystals

were carried out by High resolution X-ray diffractometer. Figure 4.3 shows

the HRXRD rocking curves recorded for rhodamine-B and malachite green

doped GPI single crystal specimens.

-200 -100 0 100 2000

600

1200

1800

2400R-B-GPI

(120) Plane

MoK

Diffr

acte

d X

-ra

y in

ten

sity [

c/s

]

Glancing angle [arc sec]

60"

27"56"

(a)

-150 -100 -50 0 50 100 1500

800

1600

2400

Diffr

acte

d X

-ra

y in

ten

sity [

c/s

]

Glancing angle [arc sec]

40"

25"

M.Grn-GPI

(120) Plane

MoK

30"

(b)

Figure 4.3 X-Ray Rocking curve of (a) Rhodamin-B and (b) Malachite

green doped GPI crystals

96

The solid line (convoluted curve) was well fitted with the

experimental points represented by the filled circles. On deconvolution of the

diffraction curve, it was clear that the curves contain additional peaks, which

are 60 and 40 arc sec away from the main peak for rhodamine-B and

malachite green doped GPI crystals respectively. These additional peaks

depict an internal structural very low angle boundary. The angular separation

between the two peaks gives the tilt angle ‘ ’ which was 60 and 40 arc sec for

rhodamine-B and malachite green doped GPI crystals respectively for the

specimens depicted in Figure 4.3. The full width at half maximum of the main

peak and the very low angle boundary are respectively 56 and 27 arc sec for

rhodamine-B-GPI and 30 and 25 arc sec for malachite green-GPI crystals.

These low values reveal the fact that both the regions of the crystal are nearly

perfect as one can expect such low values only for crystals with reasonable

quality. Though the specimen contains a very low angle boundary, the

relatively low angular spread of around 200 arc sec of the diffraction curve

and the low FWHM values show that the crystalline perfection is reasonably

good. Thermal fluctuations or mechanical disturbances during the growth

process could be responsible for the observed very low angle boundary.

Figure 4.4 shows the rocking curve recorded for 0.2 mol% of

fluorescein doped single crystal specimen. The RC contains a single sharp

peak and indicates that the specimen is free from structural grain boundaries.

The FWHM of the curve is 20 arc sec which is somewhat more than that

expected from the plane wave theory of dynamical X-ray diffraction

(Batterman and Cole 1964) for an ideally perfect crystal. The broadening of

rocking curve without the presence of any splitting can be attributed to variety

of defects like randomly oriented mosaic blocks, dislocations, Frankel defects,

implantation induced defects (due to simultaneous existence of vacancies as[

97

Figure 4.4 X-Ray Rocking curve of Fluorescein doped GPI crystal

well as interstitial defects) etc. But depending upon the nature of asymmetry,

as investigated in our earlier as well as recent articles, one can expect

predominant occupation of vacancy or interstitial defects (Krishan Lal and

Bhagavannarayana 1989, Bhagavannarayana et al 2005b, 2008, 2010, 2011a,

Kushwaha et al 2010, Bhagavannarayana and Kushwaha 2010) which can be

realized in the following way. For a particular angular deviation ( ) of

glancing angle with respect to the peak position, the scattered intensity is

much more in the negative direction in comparison to that of the positive

direction. This feature clearly indicates that the crystal contains

predominantly vacancy type of defects than that of interstitial defects. This

can be well understood by the fact that due to vacancy defects which may be

due to fast growth (Bhagavannarayana et al 2010), as shown schematically in

the inset, the lattice around these defects undergo tensile stress and the lattice

parameter d (interplanar spacing) increases and leads to give more scattered

(also known as diffuse X-ray scattering) intensity at slightly lower Bragg

angles ( B) as d and sin B are inversely proportional to each other in the

Bragg equation (2d sin B= n ; n and being the order of reflection and

wavelength respectively which are fixed). However, these point defects with

98

much lesser density as in the present case hardly give any effect on the

performance of the devices based on such crystals. More details may be

obtained from the study of high-resolution diffuse X-ray scattering

measurements (Bhagavannarayana et al 2005). If the concentration is high,

the FWHM would be much higher and often lead to structural grain

boundaries (Bhagavannarayana et al 2008). Point defects up to some extent

are unavoidable due to thermodynamical considerations and growth

conditions (Bhagavannarayana et al 2010).

Figure 4.5 shows the rocking curve recorded for, 3 mol% of

L-proline doped crystal specimen. The rocking curve was quite sharp without

any satellite peaks which may otherwise be observed either due to internal

structural grain boundaries (Bhagavannarayana et al 2005) or due to epitaxial

layer which may sometimes form in crystals grown from solution

(Bhagavannarayana et al 2006). FWHM of the rocking curve was 7.5 arc sec

for L-proline doped GPI crystal which was very close to that expected from

the plane wave theory of dynamical X-ray diffraction (Batterman and Cole

1964).

-200 -100 0 100 2000

1000

2000

3000 L-Prol-GPI

(120) Plane

MoK

Dif

fracte

d X

-ray i

nte

nsit

y [

c/s

]

Glancing angle [arc sec]

7.5"

Figure 4.5 X-Ray Rocking curve of L-Proline doped GPI crystal

99

4.3.4 Optical Spectral Analysis

The UV–Vis NIR spectrum was recorded using SHIMADZU

UV-Spectrometer 1601 in the range of 200 to 1100 nm. Optically polished

crystal plates of 2 mm thickness were used for the measurement. The

recorded spectra of dyes doped GPI are shown in Figure 4.6. The

transmittance of rhodamine-B and malachite green doped GPI crystals were

reduced to 50 % and 45 % respectively as the dyes have strong absorption in

the visible range. The absorption of 787 and 658 nm in rhodamine-B and

malachite green and doped GPI crystals respectively indicates that the

incorporation of dyes in pure GPI crystals.

Figure 4.6 UV-Visible Spectra of Pure, Rhodamine-B and Malachite

green doped GPI crystals

100

4.3.5 Raman Spectroscopic Analysis

The various functional groups of pure and L-Proline doped GPI

crystals were identified by Raman spectroscopic analysis using standard

Raman spectrometer. Recorded Raman spectrum is shown in Figure 4.7.

291

412

507

558

647

713

871

955

1032

1267

1313

1420

1540 1718

296 412

509

558

647

723

869

955

1031

1267

1314

1417

1542

1616

1655

1718

200 400 600 800 1000 1200 1400 1600 1800

0

200

400

600

800

Wavenumber (cm-1)

Pure GPI

0

200

400

600

800

1000

Ram

an

In

ten

sit

y (

arb

.un

its)

L.Prol-GPI

Figure 4.7 Raman Spectra of Pure and L-Proline doped GPI crystals

The most characteristic stretching mode ( CO) of the C=O bond

appears at 1718 cm 1. The bands in the region between 1150 and 900 cm 1

arise from the stretching vibrations of the PO3 groups and bending (in-plane

and out-of-plane) vibrations of the P–H bond. The deformation modes of the

101

PO3 group of the phosphite ions appear in the region between 600 and

400 cm 1, where the bands of the deformation (wagging and rocking) modes

of the COOH group also appear. The bonds observed at 1655 and 1616 cm-1

corresponds to C=O and NH of L-Proline molecule. This clearly indicates

the incorporation of L-proline in pure GPI crystal. The symmetric stretching

vibration of NH3+ was observed at 1540 cm-1 and 1542 cm-1 for pure and

doped GPI. Scissoring vibrations of CH2 bond was observed at 1420 and

1417 cm 1. The band at 1313 and 1314 cm 1 was assigned to the twisting

mode of CH2 vibration. The symmetric vibration of the PO2 was identified at

955 cm 1 from the spectrum. Bending mode of PH bond was found at

1031 cm 1. The band at 869 cm 1 was assigned as the stretching mode of CC

bond. Deformation vibrations of the COOH group of glycinium was observed

at 647 cm 1.Wagging and rocking vibrations of the same group were observed

at 558 and 509 cm 1. Raman shift at 412 cm 1 was assigned as the

deformation vibrations of phosphite ions and all the peak assignments are

given in Table 4.2.

Table 4.2 Assignments of Raman spectrum

Raman shift (cm-1)Pure GPI L.Prol-GPI

Assignments

1718 1718 C=O---- 1665 C=O---- 1616 NH

1540 1542 sNH3

1420 1417 CH2

1313 1314 CH2

1267 1267 C-OH1032 1031 PH955 955 sPO2

871 869 CC647 647 COOH558 558 COOH507 509 COOH412 412 sPO3

102

4.3.6 Ferroelectric Transition Temperature Analysis

Differential scanning calorimetric measurement was used to

determine the ferroelectric transition temperature of dyes and amino acid

doped GPI crystals using NETZSCH DSC 204 differential scanning

calorimeter with a cooling / heating rate of 10 K/min. DSC spectrum was

recorded in nitrogen atmosphere and is shown in Figure 4.8. An endothermic

peak at 215, 227, 226 and 236 K was observed for rhodamine-B, malachite

green, fluorescein and L-Proline doped GPI crystals respectively, which

corresponds to second-order ferroelectric transition temperature of the

materials. Thus the transition temperature was increased considerably for dyes

and amino acid doped crystals except rhodamine-B doped GPI crystal.

210 215 220 225 230 235 240 2450.35

0.36

0.37

0.36

0.38

0.36

0.37

0.30

0.32

Temperature (K)

R.B-GPI

215 K

227 K

M.green-GPI

226 K

Flrn-GPI

Heat

flo

w (

mW

/mg

)

236 K

L.Prol-GPI

Figure 4.8 DSC curve of dyes and amino acid doped GPI crystals

103

4.3.7 Piezoelectric Charge Co-efficient Measurements

Piezoelectric d33 charge coefficient for dyes and amino acid doped

GPI crystals were carried out using a Precision Piezo Meter System PM 300.

Piezo Meter was calibrated with the dynamic force of 0.25 N and the

frequency of 110 Hz. Force applied and piezoelectric charge was measured

along the (100) plane of the crystal plates. Piezoelectric d33 coefficients were

determined. Effect of poling (an electric field of 10 kV / mm for 10 minutes

duration was given to the samples) of crystals was also carried out.

Piezoelectric charge coefficients of dyes and amino acid doped GPI (unpoled

and poled) crystals were presented in Table 4.3.

Table 4.3 Piezoelectric charge coefficients (d33) of pure, dyes and amino

acid doped GPI crystals

d33 (pC/N)Crystal Before

PolingAfter DC

Poling

Pure GPI 0.87 1.03

Rhodamine B-GPI 0.30 0.56

Malachite green-GPI 0.49 0.53

Fluorescein-GPI 0.57 0.66

L-Proline-GPI 0.27 0.33

4.3.8 Ferroelectric Measurements

Ferroelectricity of the material is ascertained by P – E hysteresis

loop. Hysteresis loop (Figure 4.9) was traced for dyes and amino acid doped

GPI crystals using automatic P – E loop tracer at the temperature of 193 K

and at frequency of 50 Hz. The experiment was performed on ferroelectric

b-axis oriented (100) crystal plates of thickness 3 mm. Observed hysteresis

104

loops in present investigation are in elliptical shape which shows the

ferroelectric nature of the materials. Area of the hysteresis curve increases

along with the remanent polaristaion and coercive force with increase of

applied electric field. The squareness of hysteresis loop was determined. The

squareness parameters for rare earth metals doped crystals were found to be

nearer to 2. The ferroelectric parameters were calculated and presented in

Table 4.4.

Electric Field (kV/cm)

-15 -10 -5 0 5 10 15

Po

lari

zati

on

(µ

C/c

m2)

-8

-6

-4

-2

0

2

4

6

Pure GPI

R-B-GPI

M.grn-GPI

Flrn-GPI

(a)

Electric Field (kV/cm)

-8 -6 -4 -2 0 2 4 6 8

Po

lari

zati

on

(µC

/cm

2)

-10

-8

-6

-4

-2

0

2

4

6

8

10

Pure GPI

L-Prol-GPI

(b)

Figure 4.9 P – E Hysteresis Loop of (a) dyes and (b) amino acid doped

GPI crystals

105

Table 4.4 Ferroelectric parameters of pure, dyes and amino acid doped

GPI crystals

CrystalCoercive

Field‘Ec’ (kV/cm)

RemanentPolarization‘Pr’ µC/cm2)

SaturationPolarization‘Ps’ (µC/cm2)

Squareness ofPolarization

‘Rsq’

Pure GPI 4.73 0.82 1.02 1.90

R.B-GPI 8.71 3.03 3.9 1.88

M.green-GPI 5.91 4.14 5.07 1.92

Fluorescein -GPI

3.61 0.29 0.61 1.58

L.Prol-GPI 4.4 7.12 7.82 2.01

4.3.9 Mechanical Stability Analysis

Crystal hardness is one of the important mechanical properties of

the materials. It can be used as a suitable measure of the plastic properties and

strength of a material. Stillwell (1938) defined hardness as resistance against

lattice destruction whereas Ashby defined it as an ability of a crystal to resist

a structural breakdown under an applied stress (Karan et al 2003). This

resistance is an intrinsic property of the crystal. There are three general types

of hardness measurements depending on the manner in which the test is

conducted. These are scratch hardness, indentation hardness and rebound, or

dynamic hardness. Among these hardness measurement techniques,

indentation hardness testing is frequently used to assess the crystal hardness.

Indentation was made on dyes and amino acid doped GPI crystals

using microhardness tester MVH-1 (METATECH). The applied load was

varied from 5 g to 50 g. The indentation were approximately square in shape.

The shape of the impression is structure, face and also material dependent.

The length of the two diagonals of the indentations were measured by a

calibrated micrometer attached to the eye piece of the microscope after

unloading and the average (d) is found out. The Vickers hardness number is

106

computed using the formula Hv = 1.8544 P/d2 kg/mm2, where P is the applied

load in kilograms, d is the diagonal length of the indentation impression in

micrometers.

The mirohardness plot of dyes and amino acid doped GPI crystals

are shown in Figure 4.10. It was observed from the plot that the hardness

number increases with the load up to 20 g, which shows the work hardening

of the material. After 20 g of load micro cracks were initiated and propagated

with increase of load till 50 g load beyond which crystal gets damaged and the

measurement could not be continued. In comparison with pure GPI hardness

number improved on doping since the absorbance of dyes and amino acid into

the pure GPI lattice hampers the formation of dislocation.

Using the maximum value of hardness number ‘Hv’, the mechanical

parameter such as elastic stiffness constant ‘C11’, meyer’s index ‘n’ and yield

strength ‘ y’ were calculated and presented in Table 4.5.

0 10 20 30 40 50

30

40

50

60

70

80

90

100

110

120

130

140

Ha

rdn

ess

(H

v)

Load (g)

Pure GPI

R.B-GPI

M.green-GPI

Fluorescein-GPI

(a)

Figure 4.10 (Continued)

107

0 10 20 30 40 50

30

40

50

60

70

80

90

Ha

rdn

es

s (

Hv)

Load (g)

Pure GPI

L.Prol-GPI

(b)

Figure 4.10 Load vs Hardness plot of (a) dyes and (b) amino acids doped

GPI crystals

Table 4.5 Mechanical properties of pure, dyes and amino acid doped

GPI crystals

CrystalMaximum

value of ‘Hv’(kg/mm2)

Meyer’sindex ‘n’

Stiffnessconstant

‘C11’ (MPa)

Yieldstrength ‘ y’

(MPa)

GPI 82 1.94 2234.47 27.33

R.B-GPI 100 1.88 3162.28 33.33

M.green-GPI 100 1.97 3162.28 33.33

Fluorescein -GPI 130 1.88 5004.96 43.33

L.Prol-GPI 84 1.98 2330.71 28.00

4.4 CONCLUSION

Single crystals of dyes and amino acid doped GPI crystals were

grown by solvent evaporation and temperature lowering techniques. The

108

grown crystals were subjected to various characterizations to realize the

physical properties of doped GPI materials. Single crystal XRD results reveal

the variation of cell parameters and structural morphologies of the doped

crystals with pure GPI crystal. X-ray powder diffraction method was used to

identify the crystalline phases of dyes and amino acid doped GPI crystals.

X-ray rocking curves were plotted for doped crystals using HRXRD analysis,

which reveals the crystalline perfection of crystals. FWHM of rhodamine-B,

malachite green, fluorescein and L-Proline doped GPI crystals were 56, 30, 20

and 7.5 arc sec respectively. L-Proline doped GPI crystal are nearly perfect

single crystals without having any internal structural grain boundaries. On the

other hand, grain boundaries, low angle tilt boundaries and interstitial defects

were observed for dyes doped GPI crystal specimens. The incorporation of

dyes in the pure crystalline matrix was identified by absorption of 787, 658

nm in the UV-Visible spectrum. It was also observed that the transparency of

rhodamine-B, malachite green doped crystals were decreased considerably.

Paraelectric to ferroelectric transition temperature of pure and doped GPI

crystals was determined by DSC measurement. Transition temperature (Tc)

was improved for malachite green, fluorescein and L-Proline doped crystals

where as decreased for rhodamine-B doped crystal. Piezoelectric charge

coefficient (d33) was measured for unpoled and poled samples of doped GPI

crystals. After poling there was a slight increment in d33 values for doped GPI.

P – E hysteresis loop of pure and doped GPI crystals were measured and the

ferroelectric parameters were calculated. Mechanical stabilities of pure and

doped GPI crystals were analyzed using Vicker’s microhardness analysis and

mechanical properties of crystals were calculated.